lm4935rlx National Semiconductor Corporation, lm4935rlx Datasheet - Page 34

• Manufacturer Part Number: lm4935rlx
• Description: Audio Sub-system With Dual-mode Stereo Headphone And Mono High Efficiency Loudspeaker Amplifiers And Multi-purpose Adc
• Manufacturer: National Semiconductor Corporation

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Bits
12.0 Status & Control Registers
12.12 AGC_1 CONFIGURATION REGISTER
This register is used to control the LM4935’s Automatic Gain Control. (Note 16)
Note 16: See the AGC overview.
3:1
7:5
0
4
NOISE_GATE_ON
AGC_TARGET
AGC_ENABLE
NOISE_
THRES
GATE_
Field
If set the AGC controls the analog microphone preamplifier gain into the system. The microphone
input must be passed to the ADC.
Programs the target level of the AGC. This will depend on the expected transients and desired
headroom. Refer to AGC_TIGHT (bit 7 of 0x09h) for more detail.
If set, signals below the noise gate threshold are muted.The noise gate is only activated after a set
period of signal absence.
This field sets the expected background noise level relative to the peak signal level. The sole
presence of signals below this level will not result in an AGC gain change of the input and will be
gated from the ADC output if the NOISE_GATE_ON is set. This level must be set even if the noise
gate is not in use as it is required by the AGC algorithm.
NOISE_GATE_THRES
AGC_TARGET
TABLE 13. AGC_1 (0x08h)
000
001
010
100
101
000
001
010
100
101
011
110
111
011
110
111
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
(Continued)
34
Description
Target Level
−10 dB
−12 dB
−14 dB
−16 dB
−18 dB
−20 dB
−72 dB
−66 dB
−60 dB
−54 dB
−48 dB
−42 dB
−36 dB
−30 dB
−6 dB
−8 dB
Level